1. Field of the Invention
The present invention relates to integrated circuits and, more particularly to a bonding pad that allows for more reliable wire bonding.
2. Background of Related Art
An integrated circuit (IC) die is a small device formed on a semiconductor wafer, such as a silicon wafer. Such a die is typically cut from the wafer and then pads on the die are electrically connected to leads of a carrier or lead frame via wire bonding. The die and wire bonds are encapsulated with a protective material such that a package is formed. The leads of the lead frame protrude from the package and terminate in pins that allow the die to be electrically connected with other circuits, such as on a printed circuit board.
While the complexity of integrated circuits has been increasing, the size of such circuits has been decreasing. Further, more pads are required in a smaller area, causing the size of the pads and the space between pads to decrease. FIGS. 1A and 1B illustrate the decrease in pad size and spacing. The measurement from the center of a pad to the center of an adjacent pad is referred to as pitch. FIG. 1A is an enlarged view of a die 10 having bonding pads 12 with a 90 um pitch and FIG. 1B is an enlarged view of a die 14 having bonding pads 16 with a 50 um pitch.
Before a die is cut from the wafer on which it is formed, the die is tested by placing probes in contact with the bond pads. The probes cause marks on the bond pads. Although the size of the bond pads has decreased, probe technology has lagged behind the wire-bonding technology. That is, as the pad dimension has decreased, the size of the probe tips used for testing has remained about the same, making the pads more susceptible to being damaged by the probes. As is understood by those of skill in the art, ultra fine pitch bonding quality and reliability are affected by probe mark area and depth, and the frequency with which the pads have been probed.
FIG. 2A is an enlarged top plan view of a pair of adjacent die bonding pads 20 having probe marks 22 caused by probe tips and FIG. 2B is an enlarged view of pads 24, 26 that have been damaged by probe tips. More specifically, the metallization of the pad 24 has been punctured and the pad 26 has been cracked. Over sized probes can also form ball bonds at the probe mark area that may impede intermetallic growth.
Referring now to FIG. 3, a conventional bonding pad 30 is shown. The bonding pad 30 is formed of metal such as copper, aluminum and gold. The bonding pad 30 includes a border 32 that surrounds a perimeter of the pad 30. The border 32 is generally formed of a metal layer coated with polymide. The bonding pad 30 has a width X and a length Y. For a device having a 63 um pitch, X is about 60 um, Y is about 90 um, the border 32 is about 2 um wide, and the space between adjacent pads is about 3 um.
The inner area of the pad 30 is used to attach a connection wire (not shown) to the pad 30 using a wire bonding technique. Wire bonding is typically done using one of three industry standard techniques: thermocompression (T/C) bonding, which uses a combination of pressure and elevated temperature; thermosonic (T/S) bonding, which uses a combination of pressure, elevated temperature and ultrasonic vibration bursts; and ultrasonic (U/S) bonding, which uses a combination of pressure and ultrasonic vibration bursts.
A circular shaded area denoted 34 represents the effective diameter of a bonded ball, which is the dimension of the ball that actually contacts the pad 30. For a 63 um pitch, the required bonded ball diameter (BBD) is about 40-45 um. The inner, oval shaded area denoted 36 represents a probe mark. As previously discussed, probe marks can damage pads, causing poor quality or unreliable wire bonds.
It is an object of the present invention to provide a bonding pad that allows for more reliable wire bonding.
In order to provide more reliable wire bonds, the present invention provides an integrated circuit device bonding pad having a first area for receiving a probe tip and a second area to which a connection wire may be bonded. The first area and second area are preferably separated by a partition formed of metal.
The present invention also provides an integrated circuit device bonding pad having a first area for receiving one of a probe tip and a connection wire, and a second area continuous with the first area, the second area for receiving the other one of the probe tip and the connection wire.
The present invention further provides an improved integrated circuit bonding pad having a metal partitioning line extending from a first side of the pad to a second, opposite side of the bonding pad, the partitioning line forming a pad first area and a separate, pad second area, wherein the pad first area is for receiving a probe tip and the pad second area is for receiving one end of a bonding wire for connecting the pad to a lead frame.
In another embodiment, the present invention provides a method of testing an integrated circuit die, the die having a plurality of bonding pads, including the steps of placing a probe tip on a first area of at least one of the die bonding pads, testing the die via a test device connected to the die via the probe tip, removing the probe tip from the at least one die bonding pad upon completion of the testing step, and attaching a wire to a second area of the at least one of the die bonding pads. The second area is separate from the first area. Partitioning also provides good contrast and thus enhances the Pattern Recognition system (PRS) for the wire bonder for better bonding placement. Bonding placement is critical for Ultra Fine Pitch applications with the standard requirement that 100% of the bonded ball diameter must be within the bonding pad dimensions.